PR-102995-10 IRR to Council_FINAL_27May14

       2.1   Topography and Site Drainage
       The maximum site level is approximately 16.60m AHD, falling to 9.28m AHD over a
       distance of approximately 91m. There is an average existing gradient on site of
       approximately 8%, falling in a south-westerly direction.

       The site currently drains to a DN450 RCP pipe, which flows south to the lawful point
       of discharge for Lot 101. In this report, the upstream catchment comprising of a
       portion of the neighbouring site is included in the overall catchment calculations.

3      STORMWATER
       All stormwater drainage calculations were undertaken in accordance with the
       requirements of QUDM. The existing stormwater drainage layout for the proposed
       Lot and existing Lot 101 can be found on the attached drawing 10234.01_DA01.

       It is proposed that a 3.0m wide easement be provided over the existing stormwater
       overland flow path to the south of the site (refer Plan 10234.01_DA01). This will allow
       for unimpeded stormwater overland flow from the neighbouring property (Lot 26 on
       SP151406) through the proposed Lot 103.

       The current catchment for the existing point of discharge was calculated at 0.911ha,
       covering an area extending into the neighbouring property (Lot 26 on SP151406) as
       shown on Plan 10234.01_DA03. The total catchment discharge for a Q10 Storm event
       was calculated to be 0.329m3/s, adopting a C10 value of 0.78 and a tc of 11 minutes
       (refer Appendix D for runoff calculations for the overall catchment).

       As this application refers only to the reconfiguration of Lot 101, and does not address
       the stormwater needs of a developed site scenario, it is assumed that stormwater
       detention measures will not be required. The reconfiguration of Lot 101 does not
       worsen the current stormwater situation. However any future development that
       increases the impervious area of the catchment will require detention measures.
       Refer to Section 3.1 for information regarding assumptions made for a post-
       development scenario.

       3.1   Proposed Lot 103 Catchment
       The proposed Lot 103 catchment covers an area of 4073m2 and is currently
       vegetated. For the pre-developed scenario, a Q10 discharge of 0.137m3/s was
       established, adopting a C10 value of 0.70 and tc of 10 minutes. In the case of a future
       developed scenario, a Q10 discharge of 0.209m3/s was established adopting a C10
       value of 0.88 and an expected tc of 6 minutes. (Refer to Appendix E for discharge
       calculations).

       This change in Q10 discharge value indicates that detention measures will need to be
       implemented in the case of any development to proposed Lot 103 that increases the
       impervious area that provides an approximate total detention volume of 27.0m3.




INTELARA PTY LTD                                                                      Page 5 of 13
10234.01rb01                                                                                Rev B